#!/usr/bin/node 
//拉取流
const Readable = require('stream').Readable;
//var rs = new Readable();
//字符c，转ascii
var c = 'a'.charCodeAt(0);


class MyReadable extends Readable {
  constructor() {
    super();
  }
  _read(){
    rs.push(String.fromCharCode(c++));
    if(c > 'z'.charCodeAt(0)) {
      rs.push(null);
    }
  }
}
let rs = new MyReadable();
rs.pipe(process.stdout);
